Enteric stool specimens are frequently collected in a 10% formalin or sodium acetate-acetic acid-formalin (SAF) transport medium which serves to inactivate the infectivity and preserve the morphology of parasitic organisms in the sample. These media may have adverse effects on the function of antibodies in diagnostic immunoassays.
Formalin, also known as formaldehyde, binds to amino groups on proteins, potentially altering their structure and functional activity. Low pH, such as from the acetic acid in SAF, is inhibitory to antigen-antibody binding.
The development of an effective diagnostic immunoassay for enteric stool specimens collected in formalin or SAF, therefore, depends on the ability to counteract these adverse effects. Although some microwell and flow-through enzyme immunoassays appear to accomplish this through sample dilution, simpler and more effective approaches are needed.